Assembly and method for introducing a reducing agent into the exhaust pipe of an exhaust system of an internal combustion engine

ABSTRACT

An assembly ( 10 ) for introducing a reducing agent into the exhaust pipe ( 12 ) of an exhaust system of an internal combustion engine, in particular of a motor vehicle, has a feed connector ( 14 ) which opens into the exhaust pipe ( 12 ) and includes a wall ( 16 ), a feed device ( 20 ) for reducing agents which opens into the feed connector ( 14 ), and a device ( 22 ) for generating a gas flow (G) which is additional to the reducing agent flow (R) and lines the wall ( 16 ) of the feed 10 connector ( 14 ). Furthermore, there is described a method of introducing a reducing agent into the exhaust pipe ( 12 ) of an exhaust system of an internal combustion engine, in particular of a motor vehicle.

PRIORITY CLAIM

This application is a continuation of U.S. application Ser. No.12/670,126 filed Apr. 27, 2010, which is a national stage entry under 35USC §371(b) of PCT International Application No. PCT/EP2008/005170,filed Jun. 25, 2008, and claims the benefit of German Patent ApplicationNo. 102007034316.9, filed Jul. 24, 2007, and of German PatentApplication No. 202008001547.2, filed Feb. 4, 2008, each of which areexpressly incorporated by reference herein.

BACKGROUND

The present invention relates to an assembly for introducing a reducingagent into the exhaust pipe of an exhaust system of an Internalcombustion engine, in particular of a motor vehicle. The presentinvention further relates to a method of introducing a reducing agentinto the exhaust pipe of an exhaust system of an internal combustionengine, in particular of a motor vehicle.

To comply with specifications relating to environmental laws, exhaustgases such as those of motor vehicles driven by internal combustionengines need to be subjected to a purification. In particular, fornitrogen oxide reduction, so-called SCR catalytic converters (alsoreferred to as denitrification catalysts) are increasingly employed,which selectively reduce nitrogen oxides (NOx) generated in the engineduring combustion to form water and nitrogen with the aid of ammonia(NH₃) intermediately stored in the SCR catalytic converter. Theprovision of the ammonia required for the selective catalytic reductionis effected by a hydrolysis of urea which is added to the exhaust gasusually in a dissolved form.

Systems known from the prior art utilize an injection valve, for examplea low pressure fuel Injection valve, to introduce an aqueous ureasolution into the exhaust pipe upstream of an SCR catalytic converter.Such valves produce a fine mist of urea in the region of the valve tipwhich may deposit on the wall of the exhaust pipe. This is a problem inparticular in the low-load, low-temperature operation of the internalcombustion engine, in which the deposits are not vaporized again and maycompletely block the exhaust pipe in this way.

SUMMARY

The present invention provides an assembly and a method for introducinga reducing agent into the exhaust pipe of an exhaust system of aninternal combustion engine, which allow urea deposits to be avoided orat least greatly reduced.

In accordance with the invention, this is achieved by an assembly of thetype initially mentioned, having a feed connector which opens into theexhaust pipe and includes a wall, a feed device for reducing agentswhich opens Into the feed connector, and a device for generating a gasflow which is additional to the reducing agent flow and lines the wallof the feed connector. This additional gas flow (which is also differentfrom the main exhaust gas flow in the exhaust pipe) is at least largelyfree of reducing agent and prevents any mist produced upon injection ofa reducing agent from depositing on the walls of both the feed connectorand the exhaust pipe.

The additional gas flow may be fresh air, in particular compressed air.To this end, a compressed air pipe available in the vehicle ispreferably made use of for supplying the device.

Alternatively or additionally, the additional gas flow may be exhaustgas which is branched off from the main exhaust gas flow preferablyupstream of a turbocharger, as a result of which a desirable increasedpressure is available in the exhaust gas.

According to a preferred embodiment of the invention, the deviceincludes an inlet opening for the gas flow, which is in fluidcommunication with, e.g., a fresh air duct or with the exhaust pipe.

The inlet opening may be arranged in the wall of the feed connector. Itis also possible for the inlet opening to be formed in the region of theorifice of the feed connector into the exhaust pipe. Preferably, theinlet opening is then situated on the side of the orifice that isupstream with respect to the exhaust gas flow, that is, part of theexhaust gas flow from the exhaust pipe flows through the inlet openinginto the region of the orifice of the feed connector. According to afurther development of the invention, the device includes a guide memberwhich is arranged in the feed connector to dictate the desired directionfor the additional gas flow.

Preferably, the guide member extends from the feed device at leastpartially along the wall of the feed connector. In the region of thefeed device or a mount for the feed device, the guide member moreparticularly rests directly against the wall. This prevents any reducingagent from reaching an area between the guide member and the wall.

The guide member may line the wall of the feed connector, a gap beingformed at least in sections between the wall and the guide member.Preferably, both the wall and the guide member are of a conical shape,the wall having the larger opening angle towards the orifice. In thisway, a gap that becomes increasingly larger is produced towards theorifice of the feed connector; the additional gas flow is conductedthrough this gap.

According to one embodiment of the invention, the guide member projectsat least partially into the exhaust pipe. The guide member is made to beparticularly long here and additionally serves as a wall that is heatedby the gas flow and causes a vaporization of any deposits. As analternative, the guide member may also be configured to be very shortand serve exclusively for steering the gas flow.

Advantageously, a section of the guide member extends into the exhaustpipe on the side of the orifice that is upstream with respect to theexhaust gas flow. As already mentioned above, an inlet opening is formedin this way, which directs part of the exhaust gas flow into the feedconnector to form the additional gas flow. Alternatively oradditionally, it is, of course, also possible for a section of the guidemember to extend into the exhaust pipe on the side of the orifice thatis downstream with respect to the exhaust gas flow.

The guide member may include a continuously surrounding peripheral wall.It is likewise conceivable that the guide member lines only a partialregion of the feed connector with respect to the periphery, such as,e.g., a region that is especially susceptible to deposits.

In addition, the guide member may include one or more openings in itsperipheral wall, through which the gas flow is guided into that regionof the feed connector which is inside with respect to the guide member.Here, the use of a porous material is also conceivable. The guide membermay, of course, also be designed without any openings, i.e. closed, inparticular if it is made rather short.

The device is preferably configured such that the gas flow is formed asa swirl flowing in the feed connector, something which enhances themixing in the feed connector. This swirling of the gas flow in the feedconnector may be attained by a suitably designed and arranged guidemember and/or an oblique inlet opening.

More specifically, the feed connector is arranged at an angle of from20° to 70° in relation to the exhaust pipe, which results in aparticularly favorable distribution of the reducing agent supplied.

For a better mixing of the supplied reducing agent with the exhaust gasflow, a mixing element for causing a swirling of the exhaust gas flow isadvantageously arranged in the exhaust pipe downstream of the feedconnector.

The exhaust pipe may have a bend of approx. 20° to 70° in the region ofthe feed connector. Preferably, the bend of the exhaust pipe roughlycorresponds to the angle between the exhaust pipe and the feedconnector. It is also possible to arrange the feed connector on asection of the exhaust pipe extending in a straight line.

As already mentioned at the outset, the reducing agent more particularlyis an aqueous urea solution or a solution of other substances releasingammonia. The invention can, however, also be employed to advantage whenfuel is used as the reducing agent.

A particularly cost-effective configuration is obtained in that the feeddevice is an injection valve, in particular a low-pressure fuelinjection valve.

According to a second aspect of the invention, a method of introducing areducing agent into the exhaust pipe of an exhaust system of an internalcombustion engine, in particular of a motor vehicle, is provided. Themethod according to the invention includes the following steps:

generating a gas flow which is additional to the reducing agent flow andis at least largely free of reducing agent and lines a wall of a feedconnector opening into the exhaust pipe;

injecting the reducing agent by means of a feed device arranged on thefeed connector.

As already discussed in relation to the assembly according to theinvention, the reducing agent deposits occurring in the prior art areeffectively prevented by the method according to the invention as well.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Further features and advantages of the invention will be apparent fromthe following description of several preferred embodiments withreference to the accompanying drawings, in which:

FIG. 1 shows a schematic sectional view of an assembly according to afirst embodiment of the invention for carrying out the method accordingto the invention;

FIG. 2 shows a sectional view of an assembly according to a secondembodiment of the invention;

FIG. 3 shows a sectional view of an assembly according to a thirdembodiment of the Invention;

FIG. 4 shows a sectional view of an assembly according to a fourthembodiment of the Invention;

FIG. 5 shows a sectional view of an assembly according to the prior art,which illustrates the problem underlying the invention;

FIG. 6 shows a sectional view of an assembly according to a fifthembodiment of the invention;

FIG. 7 shows a sectional view on the feed connector according to theline VII-VII in FIG. 6; and

FIG. 8 shows an enlarged side view of the assembly according to thefifth embodiment, with the feed connector partly cut open.

DETAILED DESCRIPTION

FIG. 1 schematically shows an assembly 10 according to the invention forintroducing a reducing agent into an exhaust pipe 12 of an exhaustsystem of an internal combustion engine. In particular, the exhaustsystem of a motor vehicle is involved. The exhaust gas flow in theexhaust pipe 12 is denoted by S. The assembly 10 includes a feedconnector 14 which is of a substantially conical configuration and opensinto the exhaust pipe 12, preferably at an angle a of between 20° and70° here approx. 55° The (inside) wall of the feed connector 14 bearsthe reference number 16.

Arranged in a mount 18 provided at the end of the feed connector 14 thatis opposite to the exhaust pipe 12 is a feed device 20 for reducingagents, which opens into the feed connector 14 and which is an injectionvalve, in this case a low-pressure fuel injection valve. The reducingagent preferably is an aqueous urea solution which is introduced intothe exhaust pipe 12 upstream of an SCR catalytic converter not shown inFIG. 1. Departing from the configuration shown, it is not absolutelynecessary to provide a mount for the feed device 20; the latter may alsobe welded to the feed connector, for example. To avoid urea deposits Dwhen the urea solution is introduced, as occur in feed devices 20according to the prior art and are schematically shown in FIG. 5, theassembly 10 according to the invention (FIG. 1) includes a device 22which serves to 10 generate a gas flow G that is additional to thereducing agent flow R and lines the wall 16 of the feed connector 14.

The device 22 comprises of at least one, in the present case a pluralityof inlet openings 24 arranged in the wall 16 for the gas flow G whichinvolves fresh air, more particularly compressed air, or else exhaustgas which is branched off of the feed connector 14. The device 22furthermore comprises a guide member 26 arranged in the feed connector14.

To feed the ammonia required for nitrogen oxide reduction to an SCRcatalytic converter connected downstream of the assembly 10, accordingto the invention a gas flow G additional to the reducing agent flow R isgenerated in the region of the feed connector 14, the additional gasflow G being at least largely free of reducing agent and annularlylining the wall 16 of the feed connector. To this end the gas flow Genters through the openings 24 into the feed connector 14 and isdeflected by the guide member 26, so that the gas flow G flows along thewall 16 of the feed connector 14 and practically covers the wall 16 fromthe reducing agent flow R. At the same time, the reducing agent isinjected into the feed connector 14 and thereby into the exhaust pipe 12with the aid of the feed device 20, the guide member 26 directing thegas flow G such that the reducing agent flow R is, as it were, sheathed,and in this way preventing the fine mist of urea N developing at the tipof the feed device 20 from being able to deposit on the wall 16 or on awall of the exhaust pipe 12.

FIGS. 2 to 4 show further embodiments of the assembly 10 according tothe invention that are modified as compared with FIG. 1. Identical orfunctionally identical components will be denoted by the same referencenumbers below, and only the differences from the assembly 10 describedso far will be discussed.

In the embodiment according to FIG. 2, only one inlet opening 24 isprovided, which is again arranged in the wall 16 of the feed connector14 and is in fluid communication with a compressed air pipe of thevehicle or with the exhaust pipe upstream of a turbocharger or upstreamof the reducing agent injection. The gas flow G flows through the inletopening 24 and reaches a gap 28 formed between the wall 16 and the guidemember 26. In the embodiment shown, the guide member 26 extends from themount 18 for the feed device 20 (not shown here) along the wall 16 ofthe feed connector 14 and lines the wall 16. Just like the feedconnector 14, the guide member 26 has a conical shape, but, comparedwith the region of the feed connector 14 close to the mount 18, it has asmaller opening angle towards the orifice into the exhaust pipe 12. Inthe embodiment shown, the guide member 26 extends over the entire lengthof the feed connector 14 and in the lower, downstream region even partlyinto the exhaust pipe 12, here up to a static mixing element 30 arrangeddownstream of the feed connector 14, the guide member 26 serving as aheated wall which (in addition to directing the gas flow G) favors avaporization of any deposits.

In the region of the feed connector 14, the exhaust pipe 12 has a bendthe angle β of which likewise amounts to between 20° and 70°, here 55°.Owing to the bend of the exhaust pipe 12 and the angled arrangement ofthe feed connector 14 in relation to the exhaust pipe 12, the reducingagent flow R flows roughly perpendicularly against the mixing element30. The feed connector 14 may, of course, also be arranged on a sectionof the exhaust pipe 12 extending in a straight line (not shown).

FIG. 3 shows a further embodiment of the assembly 10 according to theinvention, in which the guide member 26 (as in the embodiment shown inFIG. 1) is of a comparatively short configuration and extends onlypartly along the wall 16 of the feed connector 14 (at least in thelower, downstream region). On that side of the orifice of the feedconnector 14 into the exhaust pipe 12 that is upstream in relation tothe exhaust gas flow S, a bent section 32 of the guide member 26 extendsinto the exhaust pipe 12 and thereby defines an inlet opening 24 whichdirects part of the exhaust gas flow S into the feed connector 14 orinto the gap 28 between the guide member 26 and the wall 16. The inletopening 24 is thus formed in the region of the orifice of the feedconnector 14 into the exhaust pipe 12 here. A separate inlet opening 24for the gas flow G is not necessary, as a result of which a particularlysimple design is obtained. As with the other embodiments shown so far,the guide member 26 has a closed peripheral wall 34.

As shown in FIG. 4, the guide member 26 may also have a plurality ofopenings 36 in its peripheral wall 34 to guide the gas flow G into theregion of the feed connector 14 that is inside with respect to the guidemember 26. Also conceivable is the use of a porous material tomanufacture the guide member 26.

According to the embodiment as shown in FIGS. 6 to 8, the device isconfigured in such a way that the gas flow G is in the form of a swirlflowing in the feed connector 14, something which enhances the mixing ofthe reducing agent R in the gas flow G as early as in the feed connector14. This swirling of the gas flow G in the feed connector 14 may beattained by a suitably configured and arranged guide member 26 and/or anoblique inlet opening. In the embodiment illustrated, the inlet opening24 into the gap 28 is positioned so as to be eccentric (see FIG. 7), sothat a swirl is already formed in the gap 28 which then impinges as suchon the reducing agent R via an annular opening 38 between the beginningof the guide member 26 and the beginning of the connector 14. As seen inFIG. 8, attached to the guide member 26 is a helically bent, shortdeflection part 27 which is located between the guide member 26 and thefeed connector 14 to direct the gas around the conical guide member 26towards the annular opening 38. The deflection part 27 is to beconsidered a section of the guide member 26. The gas for one thing mixeswith the reducing agent R and, for another thing, comes to lie againstthe inside of the tubular guide member 26, likewise in the form of aswirl. In this embodiment the guide member 26 is connected with the feedconnector 14 at some points (not shown).

The assembly according to the invention provides a solution that Issimple to manufacture and therefore cost-effective, for avoiding anyundesirable reducing agent deposits when a reducing agent Is introducedinto the exhaust pipe of an exhaust system.

In addition, it is at the discretion of a person skilled in the art toemploy all of the features described above both individually and incombination with each other to achieve the object of the invention.

The assembly 10 is an apparatus that includes an exhaust pipe 12, a feedconnector 14, and a guide means 26 as suggested in FIGS. 1-4. Theexhaust pipe 12 is formed to include an exhaust passageway 121 that isadapted to conduct an exhaust gas S to a downstream catalytic converter(not shown). The exhaust pipe 12 is formed to include a side aperture122 opening into the exhaust passageway 121 as suggested in FIGS. 1-4.

The feed connector 14 is formed to include a feed-connector channel 141and the guide means 26 is positioned to lie in and extend through thefeed connector channel 141 as suggested in FIGS. 1-4. The feed connector14 includes an inlet end 142 formed to include an inlet aperture 143adapted to receive a flow of reducing agent R comprising an aqueous ureasolution from a reducing agent source as disclosed herein, an outlet end144 formed to include an outlet aperture 145 and coupled to the exhaustpipe 12 to cause the outlet aperture 145 to open into the exhaustpassageway 121, and an inner surface 146 arranged to extend from theinlet end 142 to the outlet end 144 to define a feed-connector channel141 extending from the inlet end 142 to the outlet end 144 as suggestedin FIGS. 1-4.

The feed connector 14 has a substantially conical configuration and hasa small inlet end 142 and a relatively larger outlet end 144 assuggested in FIGS. 1-4. The feed connector opens into the exhaust pipeat an angle a of approximately 55°.

The guide means 26, sometimes called a guide member 26, is arranged tolie in the feed-connector channel 141 formed in the feed connector 14 assuggested in FIGS. 1-4. The guide means 26 is configured to providemeans for communicating the flow of reducing agent R passing through theinlet aperture 143 of the feed-connector 14 into the exhaust passageway121 via a reducing-agent passageway 261 to combine with exhaust gas Sflowing through the exhaust passageway 121 in a downstream directiontoward the catalytic converter described herein and as suggested inFIGS. 1-4. The guide means 26 includes an inner surface 262 that definesthe reducing-agent passageway 261 as suggested in FIGS. 1-4.

The guide means 26 also includes an outer surface 263 that is arrangedto cooperate with a surrounding portion of the inner surface 146 of thefeed connector 14 to define there between a gap means 28 as suggested inFIGS. 1-4. The gap means 28 is adapted to conduct a flow ofdeposit-blocking gas G along the inner surface 146 of the feed connector14 in a direction toward the exhaust passageway 121 of the exhaust pipe12 to block deposition of matter entrained in the flow of reducing agentR on or along the inner surface 146 of the feed connector 14 and on oralong an inner surface 123 of the exhaust pipe 12 that bounds theexhaust passageway 121 as described herein and suggested in FIGS. 1-4.The deposit-blocking gas G conducted in the gap means 28 is at leastlargely free of reducing agent R and annularly lines the inner surface146 of the feed connector 14 as described herein and suggested in FIGS.1-4.

The assembly 10 further comprises an ingress means 22 for admitting aflowing deposit-blocking gas G into the gap means 28 to establish theflow of deposit-blocking gas G conducted there through as describedherein and suggested in FIGS. 1-4. The ingress means 22 comprises anopening 24 formed in the inner surface 146 of the feed connector 14 assuggested in FIGS. 1-4. The feed connector 14 includes a wall 16 coupledto the exhaust pipe 12 and the opening 24 is arranged to lie inspaced-apart relation to the exhaust pipe 12 and to extend through thewall 16 as suggested in FIGS. 1-4. A portion of the outer surface 263 ofthe guide means 26 faces toward the opening 24 formed in the innersurface 146 of the feed connector 14 as suggested in FIGS. 1-4 so thatthe opening 24 opens toward a portion of the outer surface 263 of theguide means 26.

The assembly 10 also includes a feed-device means 20 for discharging thereducing agent R under pressure through the inlet aperture 143 formed inthe inlet end 142 of the feed connector 14 into the reducing-agentpassageway 261 to establish the flow of reducing agent R as describedherein and suggested in FIG.1. The feed-device means 20 is located inspaced-apart relation to the exhaust pipe 12 to locate the feedconnector 14 there between as suggested in FIGS. 1-4. The feed-devicemeans 20 is located outside of the exhaust passageway 121 formed in theexhaust pipe 12 as suggested in FIGS. 1-4.

The assembly 10 further comprises means 22 for discharging thedeposit-blocking gas G through the opening 24 formed in the wall 16 ofthe feed connector 14 to cause the flow of deposit-blocking gas G to bedeflected by the outer surface 263 of the guide means 26 and flow alongand cover the inner surface 146 of the feed connector 14 to minimizecontact of the flow of reducing agent R exiting the reducing-agentpassageway 261 with the inner surface 146 of the feed connector 14 asdescribed herein and suggested in FIGS. 1-4. The flow ofdeposit-blocking gas G is arranged to sheath the flow of reducing agentR exiting the reducing-agent passageway 261 to block a fine mist of ureaincluded in the flow of reducing agent R from depositing on the innersurface 146 of the feed connector 14 and the inner surface 123 of theexhaust pipe 12 as described herein and suggested in FIGS. 1-4.

The invention claimed is:
 1. A reducing agent injection apparatus for usexhaust system with a catalytic converter, the apparatus comprising anexhaust pipe formed to include an exhaust passageway adapted to conductexhaust gas to the catalytic converter and formed to include a sideaperture opening into exhaust passageway, a feed connector arranged toextend through the side aperture into the exhaust passageway of theexhaust pipe, the feed connector upstream of the catalytic converterincluding an inlet end formed to include an inlet aperture ad to receivea flow of reducing agent comprising an aqueous urea solution from areducing agent source, an outlet end formed to include an outletaperture and coupled to the exhaust pipe to the outlet aperture to openinto the exhaust passageway, and an inner surface arranged to exit fromthe inlet end to the outlet end to define a feed-connector channelextending from the inlet end to the outlet end, and a guide arranged inthe feed-connector channel configured to communicate the flow ofreducing agent passing through the inlet aperture of feed-connector intothe exhaust passageway via a reducing-agent passageway to combine withexhaust gas S flowing through the exhaust passageway in a downstreamdirection toward the catalytic converter, wherein the guide includes aninner surface arranged to define the red agent passageway and an outersurface arranged to cooperate with a surrounding portion of innersurface of the feed connector to define therebetween a gap configured toconduct a flow of deposit-blocking gas that is at least largely free ofreducing agent the inner surface of the feed connector to blockdeposition of matter entrained in the flow of reducing agent on or alongthe inner surface of the feed connector and an inner surface of theexhaust pipe bounding the exhaust passageway.
 2. The apparatus of claim1, further comprising an opening configured to admit the flowingdeposit-blocking gas into the gap to establish the flow ofdeposit-blocking gas conducted therethrough.
 3. The apparatus of claim2, wherein the opening is formed in the inner surface of the feedconnector.
 4. The apparatus of claim 3, wherein the feed connectorincludes a wall coupled to the exhaust pipe and the opening is arrangedto lie in spaced-apart relation to the exhaust pipe and to extendthrough the wall.
 5. The apparatus of claim 3, wherein a portion of theouter surface of the guide faces toward the opening formed in the innersurface of the feed connector.
 6. The apparatus of claim 1, wherein thefeed connector has a substantially conical configuration and has a smallinlet end and a relatively larger outlet end.
 7. The apparatus of claim6, wherein the feed connector opens into the exhaust pipe at an angle ofapproximately 55°.
 8. The apparatus of claim 1, further comprising afeed device configured to discharge the reducing agent under pressurethrough the inlet aperture formed in the inlet end of the feed connectorinto the reducing-agent passageway to establish the flow of reducingagent, wherein the feed device is located in spaced-apart relation tothe exhaust pipe to locate the feed connector therebetween.
 9. Theapparatus of claim 8, wherein the gap is located between the feed deviceand the exhaust pipe.
 10. The apparatus of claim 8, wherein the feeddevice is located outside of the exhaust passageway formed in theexhaust pipe.
 11. The apparatus of claim 1, wherein the feed connectorincludes a wall arranged to surround the guide and include the innersurface of the feed connector and the wall is formed to include anopening into the gap and further comprising a feed device configured todischarge the deposit-blocking gas through the opening formed in thewall of the feed connector to cause the flow of deposit-blocking fluidto be deflected by the outer surface of the guide and flow along andcover the inner surface of the feed connector to minimize contact of theflow of reducing agent exiting the reducing-agent passageway with theinner surface of the feed connector.
 12. The apparatus of claim 11,wherein the flow of deposit-blocking gas is arranged to sheath the flowof reducing agent exiting the reducing-agent passageway to block a finemist of urea included in the flow of reducing agent from depositing onthe inner surface of the feed connector and an inner surface of theexhaust pipe arranged to bound the exhaust passageway.
 13. A reducingagent injection apparatus for use in an exhaust system with a catalyticconverter, the apparatus comprising an exhaust pipe that defines anexhaust passageway and that is formed to include; side aperture openinginto the exhaust passageway, a feed connector arranged to extend throughthe side aperture into the exhaust passageway of the exhaust pipe, thefeed connector upstream of the catalytic converter including (i) aninlet end, (ii) an outlet end, and (iii) an inner surface arranged toextend from the inlet end to the outlet end to define a feed-connectorchannel extending from the inlet end to the outlet end, a feed deviceconfigured to discharge a flow of reducing agent under pressure throughan inlet aperture formed in the inlet end of the feed connector toestablish the flow of reducing agent comprising an aqueous ureasolution, and a guide arranged in the feed-connector channel, the guideincluding an inner surface arranged to define a reducing-agentpassageway arranged to receive the flow of reducing agent and an outersurface arranged to cooperate with a surrounding portion of an innersurface of the feed connector to define therebetween a gap configured toconduct a flow of deposit-blocking gas that is at least largely free ofreducing agent along the inner surface of the feed connector to blockdeposition of matter entrained in the flow of reducing agent on or alongthe inner surface of the feed connector.
 14. The apparatus of claim 13,further comprising an opening configured to admit the flowingdeposit-blocking gas into the gap to establish the flow of depositblocking gas conducted therethrough.
 15. The apparatus of claim 14,wherein the opening is formed in the inner surface of the feedconnector.
 16. The apparatus of claim 15, wherein the feed connectorincludes a wall coupled to the exhaust pipe and the opening is arrangedto lie in spaced-apart relation to the exhaust pipe and to extendthrough the wall.
 17. The apparatus of claim 14, wherein the opening isan annular opening formed between a beginning of the guide member wherethe reducing agent enters the reducing-agent passageway and the inletend of the feed connector where the reducing agent enters thefeed-connector channel.
 18. The apparatus of claim 13, wherein the feedconnector has a substantially conical configuration and has a smallinlet end and a relatively larger outlet end.